Various structural components, such as automotive components, require or desirably exhibit non-uniform characteristics, such as reinforced areas. There has recently evolved a composite article, commonly referred to as a tailored blank, designed to exhibit one or more different characteristics for a specific application, particularly for a structural automotive component. A tailored blank generally comprises sections which differ in one or more characteristics. Tailored blanks are typically subjected to a subsequent operation, such as stamping, to form a particular structural component.
The expression "tailored blank(s)" is understood by those having ordinary skill in the art and employed throughout this application to denote an article(s) comprising joined sections which have one or more different characteristics, preferably different thicknesses, shapes, compositions and/or properties, particularly mechanical, chemical, electrical and/or metallurgical properties. As employed throughout this application, the expression "tailored aluminum blank(s)" denotes tailored blank(s) formed from sections comprising aluminum or an aluminum-based alloy.
Tailored blanks have evolved to satisfy the need for economically manufacturing complex structural components having non-uniform characteristics. Several structural automotive components require reinforcement in certain areas. To satisfy such requirements, a tailored blank is formed by joining sections having different thicknesses or compositions. Typically, the sections are made of steel and joined by welding. In some applications, welded tailored steel blanks are required having welds of up to about 8 feet in length, typically about 2 to about 5 feet. It is difficult to produce such a long weld of steel sections having one or more different characteristics, particular different thickness and compositions, with satisfactory integrity at an economically satisfactory speed, such as about 200 to about 400 inches per minute. The welds must exhibit high quality and be free of imperfections so that the tailored blanks can undergo further forming operations, such as deep drawing and stamping.
There has also evolved the practice of utilizing scrap metal pieces to form complex structural components by welding the scrap pieces. These scrap pieces also typically exhibit one or more different characteristics, such as different thicknesses, compositions, shapes and/or properties. It is also difficult to produce acceptable structural components by welding such scrap metal pieces at an economically satisfactory speed.
Structural automotive components formed of welded tailored steel blanks have met with great success, particularly from an economic standpoint, and demonstrate great promise for further applications. See, for example, "Welded Blanks Tailor Profits," Forming & Fabricating, March 1994, pages 13-17; Wilfred Prange, "Manufacturing and Engineering Tailored Blanks" dated March 1994; and Bob H. Lewinski, "Manufacturing Systems for Tailored Blanks," March 1993. These articles disclose that tailored steel blanks are conventionally formed by laser welding or Mash-seam resistance welding. In Mash-seam resistance welding, the steel sections are subjected to continuous resistance welding and simultaneous forging. Laser welding steel sections to produce tailored steel blanks appears preferred, in that speeds of up to about 400 inches per minute have been achieved. We understand that workers in the art considered tungsten inert gas (TIG) welding undesirable for producing tailored steel blanks, in the belief that steel sections could not be TIG welded at an economically satisfactory speed.
We have recognized the advantages of tailored aluminum blanks formed by welding sections of aluminum or aluminum-alloys, which sections exhibit one or more different characteristics, such as different shapes, thicknesses, compositions and properties, such as mechanical, chemical, electrical, and/or metallurgical properties. We have also recognized the desirability of producing tailored aluminum blanks from scrap aluminum pieces with a manifest attendant economic advantage. However, we are unaware of any heretofore successful attempt to produce welded tailored aluminum blanks, or to produce welded composite aluminum articles from scrap pieces, at an economically satisfactory speed.
It is recognized in the art that techniques generally suited for welding steel can be readily adapted to welding aluminum. Accordingly, we initially believed that the welding techniques conventionally employed to produce welded tailored steel blanks could be readily adapted to produce welded tailored aluminum blanks. However, such expectations have not yet materialized.
The Mash-seam resistance welding technique employed to produce welded tailored steel blanks was not practically adaptable to produce welded tailored aluminum blanks. It was found that the electric currents were excessively high when welding aluminum, attributable to the high electrical conductivity of aluminum. Moreover, the wheels employed in Mash-seam resistance welding became coated with aluminum thereby creating a maintenance problem, attributable to the low softening temperature of aluminum. In addition, unlike steel, aluminum cannot be easily forged, attributable to the narrow plastic range of aluminum.
Attempts made to adapt laser welding to produce welded tailored aluminum blanks also have proven unsuccessful. The weld integrity of the resulting laser welds was found to be inadequate, particularly with respect to ductility. In addition, the resulting laser welds exhibited unacceptable porosity which led to cracking. The laser weld profiles were also inadequate, exhibited undercutting and surface roughness, and contained holes. Attempts to process laser welded tailored aluminum blanks by stamping and stretch forming did not yield acceptable products.
Gas tungsten arc welding (GTAW), previously and still sometimes referred to as TIG welding, is a conventional technique employed to weld various metals, including aluminum. See, for example, "Welding Aluminum: Theory and Practice," The Aluminum Association, second edition, July 1991, pages 6.14-6.19; "Welding Kaiser Aluminum," first edition, Kaiser Aluminum Chemical Sales Inc., 1967, pages 8-17 to 8-19 and 3-20 to 3-22; Metals Handbook, Volume 6, Welding and Brazing, eighth edition, American Society for Metals, pages 113-119. Connelly, U.S. Pat. No. 3,287,540 discloses TIG welding of aluminum sections. Jenkins, U.S. Pat. No. 3,421,677, discloses butt welding aluminum sections having different thicknesses by spraying metal particles. Oishi et al., U.S. Pat. No. 4,019,018, disclose TIG welding aluminum alloys employing particular electrode shapes. Hammarlind, U.S. Pat. No. 3,715,561; Jones et al., U.S. Pat. No. 3,231,332; McGinty et al., U.S. Pat. No. 3,251,977; and Harlan et al., U.S. Pat. No. 3,570,109 relate to the shape of electrodes employed in TIG welding. Arikawa et al., U.S. Pat. No. 3,351,734; Koch et al., U.S. Pat. No. 3,258,185; Normando et al., U.S. Pat. No. 3,839,619; Smith, U.S. Pat. No. 2,362,505; and Kuder, U.S. Pat. No. 4,182,951, relate to the design of a back-up bar or plate employed during welding. Notwithstanding conventional technology relating to welding and welding aluminum, we are unaware of any previous successful attempt to produce welded tailored aluminum blanks or a welded composite comprising aluminum scrap pieces.